There are more than 2 million cases of traumatic brain injury (TBI) in the United States each year with 500,000 of these cases requiring admission to the hospital. Although there have been a number of studies done on the "neurobehavioral" aspects of TBI, relatively little attention has been paid to syndromic psychiatric disorders. Preliminary work has demonstrated that the syndrome of major depression occurs in approximately one-quarter of patients hospitalized with TBI, and that the frequency of depression is related to both location of brain injury and severity of impairment. Furthermore, the duration of depression is closely related to the adequacy of social support and lesion location. Fully, the existence of depression was found to predict both recovery in activities of daily living and social functioning. Two prospective studies will independently assess the importance of mood disorders on the two-year outcome of patients with TBI, and determine the effect of antidepressant treatment on the one-year outcome of depressed TBI patients. A two-year surveillance study will ascertain the prevalence of mood disorders in trauma patients with and without brain injury (specifically, moderate or severe head injury); examine the clinical characteristics, longitudinal course, and clinical.pathological correlates of mood disorders in this population; and determine the impact of these disorders on recovery of function. In this study, 140 consecutive cases of TBI and 50 trauma control patients will be assessed for mood and physical, cognitive, and social functioning at intake and 3, 6, 12, and 24 months. Next, a treatment study which employs a double-blind placebo design will investigate the efficacy of paroxetine, a serotonin reuptake inhibitor (SSRI), to improve depression and promote recovery in 104 depressed TBI patients during 12 weeks of treatmentrevious studies of mood disorders following TBI, we have identified two types of depression: the endogenous type is characterized by brief duration and strong association with left anterior brain injury: the psychological type, by longer duration and strong association with adequacy of social support. The current proposal tests this characterization against a new and larger data set. Moreover, improved MR imaging methodology and a functional measure of neurotransmitter activity are used to examine mechanism and test the hypothesis that endogenous but not psychological depression involves strategic brain lesions which interrupt biogenic amine systems.